1. Field of the Invention
The present invention relates to a non-volatile record medium, a recording method, and a recording apparatus that allow digital audio data that has been compressed at a variable rate to be block-segmented corresponding to the data length of an encoding process, the data unit of an editing process, and a recordable time.
2. Description of the Related Art
EEPROM (Electrically Erasable Programmable ROM) that is an electrically rewritable non-volatile memory requires a large space because each bit is composed of two transistors. Thus, the integration of EEPROM is restricted. To solve this problem, a flash memory that allows one bit to be accomplished with one transistor using all-bit-erase system has been developed. The flash memory is being expected as a successor of conventional record mediums such as magnetic disks and optical discs.
A memory card using a flash memory is also known. The memory card can be freely attached to an apparatus and detached therefrom. A digital audio recording/reproducing apparatus that uses a memory card instead of a conventional CD (Compact Disc:Trademark) or MD (Mini Disc:Trademark) can be accomplished.
A file management system used for a conventional personal computer is named FAT (File Allocation Table). In the FAT system, when a particular file is defined, predetermined parameters are successively set to the file. Thus, the size of a file becomes variable. One file is composed of at least one management unit (sector, cluster, or the like). Data corresponding to the management unit is written to a table referred to as FAT. In the FAT file system, a file structure can be easily formed regardless of the physical characteristics of a record medium. Thus, the FAT file system can be used for a magneto-optical disc as well as a floppy disk and a hard disk. In the above-mentioned memory card, the FAT file system is used.
However, a CD on which audio data is recorded does not have the concept of the FAT system at all. In the era of the MD with which audio data can be recorded and reproduced, music programs are recorded and edited using an FAT modified system called Link-P. Thus, the system itself can be controlled with a low power CPU. However, using such a system, data cannot be exchanged with a personal computer. Thus, the MD system has been developed as an isolated AV system.
Audio data recorded on an MD is sampled with 16 bits at 44.1 kHz. 512 samples of audio data are compressed to 212 bytes. Thus, the following relation is satisfied.212×8/(512×16)=0.21In other words, audio data recorded on an MD is compressed so that the data amount of the compressed audio data becomes around ⅕ of the data amount of the original data. The data value of 212 bytes basically depends on the sector structure of a record medium. In other words, as long as the data value is an integer, one of 211 bytes, 212 bytes, 213 bytes, 214 bytes, and 215 bytes can be selected.
In recent years, with respect to digital recording of music data, the rights of copyright owners should be adequately protected. In other words, using technologies of personal computers, digital music data can be easily copied. To prevent digital music data from being illegally copied, a next generation audio data that is encrypted has been proposed.
When audio data is encrypted corresponding to DES (Data Encrypting Standard), after audio data is compressed, it is encrypted. Since an encrypting key used in the encrypting process has around 64 bits (=56 bits+8 bits (CRC) (thus, 8 bytes)), when audio data is encrypted with the 64-bit key, because of the data unit of the compressing process, factions take place. For example, in the case of audio data of an MD, since 212/8=26.5, when the encrypting process is performed 27 times, data becomes insufficient.
To compensate the insufficient data, when four-byte data is added as dummy data, the problem of fractions can be solved. However, a data loss of around 2% (4/212=0.019) takes place. When 215 bytes are selected as the compression data unit, dummy data of seven bytes is required. The data loss amounts to around 3.3% (7/215=0.0326). When a memory card of 64 Mbytes is used, the data loss of 3.3% is equivalent to data of 2.1 Mbytes. At the present time, such a data loss is a critical problem in such an expensive memory card.
Although dummy data added for fractions may be used as sub-data having secondary information, since it is troublesome to manage dispersed data, this method will not be effective countermeasures.